This invention relates to machine tools and more particularly, compact components for machine tools which create simultaneous linear and rotary movement of tools or workpieces.
A typical machining operation, such as drilling or tapping, requires that a cutting tool, such as a drill or tap, be rotated at a predetermined speed and advanced at a predetermined feed rate toward the workpiece in order to perform the machining operation. In conventional production environments, it is desirable to perform the operation as quickly as possible to minimize idle time and reduce costs. Consequently, it is important that the tool approach the workpiece at as high a feed rate as possible until just prior to contact with the workpiece and after the operation is completed, that the tool retract from the workpiece at as high a feed rate as possible. During machining, the rotational speed and feed rate of the tool are chosen to achieve optimal cutting performance and minimal tool wear. Unfortunately, conventional machine tools generally do not have a wide dynamic range of feed rates which are effective to reduce approach and retract times and thus minimize idle time.
Conventional machine tools typically include an electric, hydraulic or pneumatic motor which is connected, either directly or by gears or belts, to a drive shaft to produce rotary motion. The drive shaft, the motor and any intervening transmission is then coupled to a pneumatic or hydraulic cylinder or other linear actuator to provide the linear motion necessary for the desired feed rates. A chuck or other tool holding device can be coupled to the drive shaft for mounting a tool or workpiece.
Other prior art devices, such as U.S. Pat. No. 3,407,680 to Westmoreland, utilize two motors and a drive shaft to produce linear motion. One motor drives a ball screw engaging a helical race on one portion of the drive shaft to produce linear motion. The second motor drives a ball spline engaging a spline on a separate portion of the drive shaft to increase the rational speed of the shaft, with the net effect to increase the dynamic range of linear motion of the shaft. The end of the drive shaft is typically fitted with a device which transmits linear motion but does not transmit the rotary motion of the shaft. Because the helical race and the spline are on separate portions of the drive shaft, these devices are not compact and have a limited range of linear motion.
One of the significant disadvantages of the prior art devices is that they are large and bulky. Because of their size, they require a large supporting frame, they are difficult to manipulate during use and they limit the size of tools and workpieces that can be used. In addition, the prior art devices are mechanically and electrically complex, therefore have poor reliability and are difficult to maintain and repair. In addition, attempts to produce compact, light weight designs have resulted in devices that are less accurate and have a limited range of rotational speeds and feed rates.
Accordingly, it is an object of this invention to provide an improved mechanism for creating simultaneous rotary and linear motion.
It is another object of the invention to provide a compact mechanism for creating simultaneous rotary and linear motion.
It is yet another object of the invention to provide an improved mechanism for creating simultaneous rotary and linear motion which has a greater dynamic range of rotational speeds and feed rates.